The present invention relates to a dynamic random access memory having open bit line architecture, and more particularly to a dynamic random access memory with open bit line architecture in which pitch of memory cells becomes nothing to do with pitch of sense amplifiers.
Generally, open bit line type dynamic random access memory (open type DRAM) is of the structure that two groups of bit lines are extended in the opposite directions from sense amplifiers disposed at the center of two groups of bit lines.
Since memory cells can be disposed at all intersecting points of word lines and bit lines in open-type DRAM, it is advantageous to have high density packaging. In other words, more memory cells can be positioned in a predetermined area on a semiconductor chip, compared with other type DRAM, i.e., folded bit line type DRAM in which two groups of bit lines are extended in the same direction from sense amplifiers.
Although open type DRAM has the above-stated advantage, it has the following disadvantage. As apparent from FIG. 1, an open type DRAM, generally, has sense amplifiers 101, 102 . . . , two groups of bit lines 201, 202 . . . , and 301, 302 . . . which are extended in the opposite direction from said sense amplifiers 101, 102 . . . , and memory cells 401, 402 . . . which are disposed at all intersecting points 501, 502 . . . of said bit lines 201, 202 . . . , 301, 302 and word lines 601, 602 . . . In such an open type DRAM, the number of memory cells counted along one of word lines 601, 602, . . . must be the same as the number of sense amplifiers 101, 102 . . . In other words, pitch of adjacent sense amplifiers has some close relation to pitch of adjacent memory cells disposed along word line.
Generally, several transistors (e.g., six transistors) are necessitated to form a sense amplifier, whereas a memory cell is formed by one transistor and one capacitor. Therefore, if size of memory cells is extremely reduced to obtain high density thereby producing DRAM with large capacity, the pitch of adjacent memory cells disposed along a word line becomes considerably smaller than the pitch of sense amplifiers. However, since the pitch of adjacent memory cells has close relation to the pitch of sense amplifiers, size of entire DRAM can not be reduced so much, although the pitch of memory cells can be considerably minimized.